The aim of the reforms brought in after a review by Lord Bonomy was to give "greater certainty" for victims and witnesses required to attend the High Court than the previous system as well as reduce adjournments and "churn" in the system.

As a result of his recommendations, the 110-day rule, frequently referred to as the "jewel in the crown" of Scots law, was extended.

The time limit within which accused in custody must be brought to trial became 140 days instead of 110.

The changes, which included the introduction of mandatory pre-trial hearings for all cases, were designed to streamline the work of some of Scotland's highest courts.

Indeed, an independent evaluation carried out by Aberdeen University in 2007 found that the situation was markedly improved for witnesses as a result - with only 1295 witnesses inconvenienced by trial adjournments in the year from April 2005, down from 16,795 in the previous 12 months.

However, victims and suspects may be forced to wait for longer. Paul McBride, a senior QC, said it is now almost unknown for a trial to start on time.

"It has succeeded in reducing the amount of time wasted for witnesses but has been spectacularly unsuccessful in relation to delays and the time people are forced to spend in custody," he said.

"There are endless motions to adjourn. Both victims and suspects are waiting a lot longer to get justice. It is not what Bonomy wanted but the truth is that it comes down to money. We need more courts, more judges and more resources for Crown Office."

While mid-trial adjournments are different to extensions in the time limits, the figures do indicate substantial delays in a system that is supposed to have been fixed.

The figures reveal that between August 2007 and August 2008 some 23% of the 797 trial indictments, involving cases such as rape and murder for which the accused would be in custody, involved applications to extend the 12-month time limit. Between April 2008 and April 2009 that rose to more than half.

Donald Findlay QC, a senior defence advocate, said: "There is no doubt that at the present moment in time it is difficult, if not impossible, to get a trial to start within the 140-day limit.

"There are a number of reasons for that. One is certainly that the new court diary system simply does not work. It is unrealistically rigid.

"A case might be set down for eight days but finishes in five and then the court lies empty for those three days. Roll that out across the country and there will be a lot of court rooms empty. Too much emphasis has been placed on cutting costs at the expense of the system - 110 days has already been extended to 140 and now it is being largely ignored."

Frances McMenamin, QC, added: "I would agree wholeheartedly and the judges seem to be concerned about the fact that time limits seem to count for nothing now."

Richard Baker, Labour's Justice spokesman, said: "The number of extensions that the Crown have applied for shows the pressure the Crown Office and Procurator Fiscal Service is under. I worry that eventually we could be in a situation where a judge deserts a case because of continual delays.

"We cannot have a situation where people avoid justice due to lack of resources.

A spokesman for the Crown Office: "The High Court deals with the most serious offences and it's vital that prosecutors have the necessary tools to do their job.

"In 2003 to 2004, 44,464 witnesses in the High Court were recited to a subsequent trial diet. In 2008 to 2009, this number was 3120 - a reduction of 93%.

"We prioritise the prosecution of serious crime in order to ensure that all time limits are complied with.

"Extensions to time limits are granted by the court only where this is considered to be in the interests of justice.

"There are good reasons for this, for example in complex or large cases or where the accused's legal representatives need further time to prepare."

A Scottish Government spokesman said: "The Bonomy reforms have been a considerable success and have continued to significantly reduce the number of trials adjourned in the High Court.

"This increased efficiency and certainty reduces the stress and inconvenience caused to the victims and witnesses of crime. These reforms were fully supported by all of the major parties."

Justice timelineApril 2005 to April 2009:1147 extensions of time recorded - 1115 requested by the Crown, 4 by the defence and 25 on joint motion and 3 "other". 58 applications for extensions of the 110-day time period prior to the fixing of the preliminary hearing.

August 2007 to August 2008:797 trial indictments and 183 applications to extend the 12-month time limit.

April 2008 to April 2009:800 trial indictments and 477 applications to extend the 12- month time limit.

August 2008 to April 2009:31 applications for extensions of the 110-day time period prior to the fixing of the preliminary hearing. 442 extensions of time recorded by the Scottish Court Service - 423 requested by the Crown, one by the defence and 18 on joint motion